An engine is provided that utilizes an active heat exchanger such as a heat pump to transfer heat into and remove heat from a low boiling point liquid that is disposed in a pair of diametrically opposed containers. The addition of heat into the low-boiling point liquid causes the liquid to move vertically from a bottom container to a top container, transforming the transferred heat energy into potential energy. The top container is allowed to fall under the weight of the transferred liquid, transforming the potential energy to kinetic energy which is used to perform the desired work. The expanding low-boiling point liquid can also be used to advance a magnetic back and forth through a wire coiling to produce an electric current, converting the transferred heat energy into electrical energy. The use of an active heat exchanger such as a heat pump permits the use of one unit of electrical energy to transfer 3 to 5 units of heat energy.